linux-kernel - Re: [PATCH v2 09/10] sched/psi: per-cgroup PSI stats disable/re-enable interface

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Date:   Tue, 23 Aug 2022 14:18:21 +0800
From:   Chengming Zhou <zhouchengming@...edance.com>
To:     Michal Koutný <mkoutny@...e.com>,
        Johannes Weiner <hannes@...xchg.org>
Cc:     Tejun Heo <tj@...nel.org>, corbet@....net, surenb@...gle.com,
        mingo@...hat.com, peterz@...radead.org, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, songmuchun@...edance.com
Subject: Re: [PATCH v2 09/10] sched/psi: per-cgroup PSI stats
 disable/re-enable interface

On 2022/8/15 21:23, Michal Koutný wrote:
> On Wed, Aug 10, 2022 at 11:25:07AM -0400, Johannes Weiner <hannes@...xchg.org> wrote:
>> cgroup.pressure.enable sounds good to me too. Or, because it's
>> default-enabled and that likely won't change, cgroup.pressure.disable.
> 
> Will it not change?
> 
> I'd say that user would be interested in particular level or even just
> level in subtree for PSI, so the opt-out may result in lots of explicit
> disablements (or even watch for cgroups created and disable PSI there)
> to get some performance back.
> 
> I have two suggestions based on the above:
> 1) Make the default globally configurable (mount option?)
> 2) Allow implicit enablement upon trigger creation
> 

I think suggestion 1) make sense in some use case, like make per-cgroup
PSI disabled by default using a mount option, then enable using the
"cgroup.pressure" interface.

But suggestion 2) auto enable upon trigger creation, if we hide the
{cpu,memory,io}.pressure files when disabled, how can we create trigger?

Want to see what do Johannes and Tejun think about these suggestions?

Thanks.